DID YOU TRY A DIFFERENT NETWORK CABLE ON THAT PC? If its saying that the network cable is unplugged, either the cable is bad, or one of the jacks is faulty. Make sure there is no dust or lint or foreign objects in either of the network jacks, and no bent or broken pins. Also look at the network cable your using to see if its damaged. Is it a store bought cable or did some one ,make it for you. Try plugging the PC into jack 3 or 4 on the router. It doesn't matter what jack you use as long as its one of the LAN jacks.